Tubes for Modulus 3A

I didn't try the tubes from my other preamp as I had already installed it in my office system. The sound seems to be getting better as the tubes break in, There is definitely more detail than my Modulus 3 had and the bass is tight, but not full. Rest of the system is Classe 15 (175wpc) amp, Vandersteen 2ce signature speakers, Raysonic 168 cd player, Marantz 8001 sacd player, Magnum Dynalab tuner. All cables and speaker wire are MIT Terminator 2, and power cords and conditioning is courtesy of Shunyata.

Have you tried a pair of Mullards? Though a little pricey there are bargains around. The Modulus pieces are hard on tubes from what I read.

Tungsram 6922s are cool!!!

That's one tube I NEVER skimp on. Manufacturers used the 6922 because of its quality compared to a 12ax7 and such. Good 6922 can make or break a system. You don't need to break the bank but $100 pair is well worth it, amperex, mullard or such. I actually like Golden Dragons if you can find them.
Keep in mind that 6922's will last up to 10,000 hours. Much longer than other types.

I previously owned a Modulus 3. The prior owner inserted a brand new quad of National 6922 tubes. I got less than 300 hours out of the new tubes. They became microphonic. I sold the preamp and the buyer tested the tubes and confirmed they were spent. I think AI recommends Russian tubes which are known to endure inspite being run at the limit. There's no reason for a preamp (properly designed) to cook tubes this way. Not meaning to put down your choice of preamp - they do sound nice. I just could not see retubing yearly. Mullards or Amperex may sound nice but probably will not last long in these preamps. A costly affair over time.